The power consumption of transistor-based system components (such as analog, digital, or mixed-signal integrated circuits or chips) may be classified into different categories based on the nature of the power consumed. Dynamic power consumption, for example, is related to moment-to-moment transistor function and depends on such factors as switching frequency and the number of transistors switching (for digital systems), power output and bias levels (for analog systems), or both (for mixed-signal systems). In general, dynamic power consumption is independent of process and temperature variations and is approximately equal to C×VDD2×f for a given capacitance C, power supply voltage VDD, and switching frequency f.
Leakage power consumption, on the other hand, is largely independent of transistor operation and is instead exponentially dependent upon process, voltage, and/or temperature. As transistors shrink, and as more transistors are used on a chip, the effects of leakage power consumption become more and more significant.
For example, the speed of a complementary metal-oxide-silicon (CMOS) integrated circuit is largely determined by the threshold voltages of its n-type (NMOS) and p-type (PMOS) transistors (i.e., lower threshold voltages allow faster switching times). FIG. 1 shows a typical. Gaussian statistical distribution 102 for threshold voltages across a sampling of transistors produced by a typical integrated-circuit manufacturing process. As the distribution 102 shows, most transistors have a typical threshold voltage, and the number of transistors decreases as the threshold voltage increases or decreases from typical.
Because integrated circuits are typically designed to operate under a variety of conditions, the voltage and frequency of operation may be chosen so that devices at the slow process corner 104 will operate reliably. This selection, however, means that the majority of devices that do not lie at the slow process corner 104 will operate with a greater VDD than necessary, thereby increasing both their dynamic and leakage power consumption (which, as described above, are both strongly dependent on VDD). In particular, devices at the fast process corner 106 (having relatively low threshold voltages) will exhibit the maximum leakage current. The leakage power consumption in the fast process corner 106 is typically 30 to 50 times that in the slow process corner 104. In addition to consuming unnecessary power, devices operating at the fast process corner 106 will also produce additional heat. The design of some integrated-circuit components, such as the package unit, is sensitive to thermal characteristics, and the cost of these components may increase due to the additional heat produced at the fast process corner 106.
Because power consumption has become a greater concern for low-power portable electronic devices (such as cellular/mobile phones, portable music players, netbook/notebook computers, portable video players, and the like) as well as for nonportable devices (such as desktop computers, embedded computers, servers, and switches), the prior-art method of fixing VDD and frequency to suit the worst-case corner is no longer tenable. Clearly, a need exists for a way to reduce both dynamic and leakage power consumption.